1. Field of the Invention
The present invention relates to a vibration gyroscope and, more particularly, to a vibration gyroscope for detecting rotational angular velocity using, for example, mechanical vibration.
2. Description of the Related Art
FIG. 5 is a diagram illustrating an example of a conventional vibration gyroscope. A vibration gyroscope 1 comprises a vibrator formed of a vibration element 2 in the shape of, for example, a regular triangular prism, and piezoelectric elements 3a, 3b and 3c formed on the sides of the vibration element 2. The piezoelectric elements 3a and 3b are used for detection to detect a signal corresponding to a rotational angular velocity. The piezoelectric element 3c is used for driving to flexibly vibrate the vibration element 2.
The piezoelectric elements 3a and 3b are respectively connected to I-V conversion circuits 4a and 4b so that the output currents of the piezoelectric elements 3a and 3b are converted into voltages. The I-V conversion circuits 4a and 4b are connected to an adder circuit 5. The output signal of the adder circuit 5 is fed back to an oscillation circuit 6, causing the oscillation circuit 6 to provide a drive signal to the piezoelectric element 3c for driving. The oscillation circuit 6 comprises, for example, a phase circuit 6a and an amplifier circuit 6b, and adjusts the phase and voltage of a signal fed back from the adder circuit 5. Further, the I-V conversion circuits 4a and 4b are connected to a differential amplifier circuit 7, and the differential amplifier circuit 7 is connected to a synchronization detection circuit 8.
As a result of supplying a drive signal output from the oscillation circuit 6 to the piezoelectric element 3c, the vibration element 2 of the vibration gyroscope 1 flexibly vibrates in a direction intersecting at right angles to the surface on which the piezoelectric element 3c is formed. At this time, the flexed states of the piezoelectric elements 3a and 3b for detection are the same, and the same signal is output from the I-V conversion circuits 4a and 4b. Therefore, the output signal of the differential amplifier circuit 7 becomes "0", and it can be seen that no rotational angular velocity is applied. When a rotational angular velocity is applied to the vibration gyroscope 1, the flexing direction of the vibration element 2 varies due to a Coriolis force. For this reason, the flexed states of the piezoelectric elements 3a and 3b vary, causing one of the output currents from the piezoelectric elements 3a and 3b to increase and the other to decrease. Therefore, the output voltages of the I-V conversion circuits 4a and 4b vary, causing the differential amplifier circuit 7 to output a signal corresponding to a change in the outputs of the I-V conversion circuits 4a and 4b. By detecting this signal using the synchronization detection circuit 8, a signal corresponding to the rotational angular velocity can be obtained.
When a rotational angular velocity is applied to the vibration gyroscope 1, the output voltages of the I-V conversion circuits 4a and 4b are each increased or decreased. However, by synthesizing these signals with the adder circuit 5, the amounts of the change in the signals are cancelled, and a signal having an almost constant voltage can be obtained. Therefore, by adjusting the phase and voltage of the output signal of the adder circuit 5 by the oscillation circuit 6, it is possible to provide a stable drive signal to the vibrator.
FIG. 6 is a diagram illustrating another example of the conventional vibration gyroscope. A vibration gyroscope 1 comprises a vibrator formed of a vibration element 2 in the shape of, for example, a regular triangular prism and piezoelectric elements 3a, 3b and 3c formed on the sides of the vibration element 2. The piezoelectric elements 3a and 3b are used for detection to detect a signal corresponding to a rotational angular velocity. The piezoelectric element 3c is used for driving to flexibly vibrate the vibration element 2.
The piezoelectric elements 3a and 3b are connected to voltage detection circuits 104a and 104b, respectively, whereby the output voltages of the piezoelectric elements 3a and 3b are detected, respectively. At this time, in order to detect the output voltages of the piezoelectric elements 3a and 3b, resistors are connected between the input ends of the voltage detection circuits 104a and 104b and intermediate points of the power supply voltage. As the voltage detection circuits 104a and 104b, buffer circuits or the like are used. The voltage detection circuits 104a and 104b are connected to the adder circuit 5. Then, the output signal of the adder circuit 5 is fed back to the oscillation circuit 6, causing the oscillation circuit 6 to provide a drive signal to the piezoelectric element 3c for driving purposes. The oscillation circuit 6 comprises, for example, a phase circuit 6a and an amplifier circuit 6b, and adjusts the phase and voltage of a signal fed back from the adder circuit 5. Further, the voltage detection circuits 104a and 104b are connected to a differential amplifier circuit 7, and the differential amplifier circuit 7 is connected to a synchronization detection circuit 8.
As a result of supplying a drive signal output from the oscillation circuit 6 to the piezoelectric element 3c, the vibration element 2 of the vibration gyroscope 1 flexibly vibrates in a direction intersecting at right angles to the surface on which the piezoelectric element 3c is formed. At this time, the flexed states of the piezoelectric elements 3a and 3b for detection are the same, and the same signal is output from the voltage detection circuits 104a and 104b. Therefore, the output signal of the differential amplifier circuit 7 becomes "0", and it can be seen that no rotational angular velocity is applied. When a rotational angular velocity is applied to the vibration gyroscope 1, the flexing direction of the vibration element 2 varies due to a Coriolis force. For this reason, the flexed states of the piezoelectric elements 3a and 3b vary, causing one of the output voltages from the piezoelectric elements 3a and 3b to increase and the other to decrease. Therefore, the output voltages of the voltage detection circuits 104a and 104b vary, causing the differential amplifier circuit 7 to output a signal corresponding to a change in the outputs of the voltage detection circuits 104a and 104b. By detecting this signal using the synchronization detection circuit 8, a signal corresponding to the rotational angular velocity can be obtained.
When a rotational angular velocity is applied to the vibration gyroscope 1, the output voltages of the voltage detection circuits 104a and 104b are each increased or decreased. However, by synthesizing these signals by the adder circuit 5, the amounts of changes of the signals are cancelled, and a signal having an almost constant voltage can be obtained. Therefore, by adjusting the phase and voltage of the output signal of the adder circuit 5 by the oscillation circuit 6, it is possible to provide a stable drive signal to the vibrator.
However, even if the vibrator is flexibly vibrated with a stable drive signal, a signal output from the vibrator becomes unstable due to environmental changes such as atmospheric temperature, or changes in vibrator characteristics and therefore, it is not possible to accurately detect rotational angular velocity.